Method and apparatus for sound reproduction



May 7, 1940. I STEUBE 2,200,106"

METHOD AND APPARATUS FOR soum: REPRODUCTION Filed Aug. 3, 1938 Snventor Fritz :S'teuhe (Ittorneg Patented May 7, 1940 PATENT OFFICE] 4 METHOD AND APPARATUS OR. SOUND! REPRODUCTION Fritz Steube, Leipzig, Germany, assignor' to Klangfilm G. M.B. H., Berlin, Germany,a corporation of Germany Application August 3, 1938, iserial No. 222,923

' In Germany August 6, 1937 7 Claims. (01. 179-1003) This invention relates to an improved method of and apparatus. for sound reproduction from film; sound records and more particularly to a method f such reproduction providing improved volume range. i

' In'practically all sound recording, it is necessary to compress the volume range of the recorded sound either automatically through proper control circuits or manually by means of appropriate volume control attenuators, or the likeyin order to bring the recording within the range of reproduction of the film, which is usually considerably less than the volume range of the original sounds produced -for example, by

l transmitting capacity of the film and the sensii large orchestras or choruses. The minimum amplitude on the sound record is determined by such factors as noise in the electrical circuits and ground noise on thefilm, while themaximum amplitude is similarly determined by the light tivity of the reproducing apparatus. In general, the'range is determined by the ratio of the maximum quantity of modulated light transmitted by the filmtothe minimum quantity of modulatedlight transmitted by the film without appreciable modulation from ground noise and of a sufficient intensity so that the modulation is greater than the inherent noises of the amplifiers.

It isknown in the prior art as, for example, in Hanna Patent No. 1,888,724, to apply volume expansion in reproducing a record which has been made with volume compression. In such an arrangement the amplification is increased as the volume level produced from the sound record is increased witha consequent overall increase in volume range. requires special equipment and usually a sound record especially made therefor.

The present invention relates to an improved reproducing-device for producing such volume expansion in any ordinary type of sound record fwhether recorded with volume compression or with manual monitoring, whether recorded with ground noise reduction or not and without the provision of any special amplifying apparatus orvelope of the sound record, and the second time being modulated in accordance with the sound waves, this result being accomplished by a single beam of light transmitted through a single Such reproduction, however,

- through a sound record and a volume control record, such as is'known in the prior art.

One object of the invention is to provide an improved sound reproducing apparatus.

Another object of the invention is to provide a sound reproducing apparatus providing increased volume rangeQ Another object of the. invention is to provide an improved soundreproducing optical system.

Anotherv object of the invention is to provide a sound reproducer wherein the scanning beam is transmitted twice through a single sound record.

Other and incidental objects of the invention will be apparent to those skilled in the art from a reading of the following specification and an inspection of the accompanying drawing, in which T Figure 1 is a schematic elevation of my improved optical system; v

t Figure 2 shows the sound track of a variable area sound record with ground noise reduction and the relationof the scanning beam theretoon its several passages,

Figure 3 shows a variable area sound record without ground noise reduction, the relation of the scanning and the relation of the scanning beam thereto on its several passages, and

Figure 4 shows in elevation the shape which may be given to lens 1 or to a diaphragm adjacent thereto in order to control the rate of change of. the light beam.

Referring to Fig. 1, the film I carries a sound record of any customary type reproduciblephotoelectrically, s'uch, for example, as the sound rec- 0rd shown in Fig. 2;

The sound record shown in Fig. 2 is of the type made, for example, in accordance with McDowell Patent 1,856,197, issuedApril 26, 1932, and includes a dark portion 2 having a marginal contour corresponding to the sound waves, and a second darkened portionv 3 having a marginal contour corresponding to the envelope of the sound waves. The light passes through the transparentportion between thesetwo darkened or opaque portions in order .to reproduce the sound and is modulated both in accordance with the sound frequencies and in accordance with the envelope of the sound frequencies.

Referring again to Fig. 1, light from an exciter lamp of any usual type as indicated at 4 passes through the condenser lens 5 where it is directed vto a slit plate having therein a slit or elongated narrow aperture 6. Light transmitted the same film area and photoelectric means for Having now described my invention, 1 claimz 1. The method of producing volume expansion. in the reproduction of photophonographic records comprising the steps of directing a relatively large converging beam of light througha film and thereafter directing the beam of light in the form of a fine line through the same film area to a photoelectric reproducer, the'convergence 'of the beam on its first passage through the film being such as to bring it to focus on-the-film in its second passage. I

2. The method of reproducing photophonographic sound records comprising the steps of directing a beam of light in the form of a relatively large converging beam through the sound record whereby the quantity of light is modulated in accordance with the average transmission of the sound record and also directing the same beam of light throughthe sound record in the form of a narrow line whereby the'beam is.

also modulated in accordance with the sound waves to be reproduced, the convergence of the beam on its first passage through the film being such as to bring it to focus on the film in its second passage.

3. Sound reproducing apparatus comprising means for directing'a converging beam of light through the film, reflecting means for redirecting the light in the form of a fine line through receiving the beam after its second passage through the film, the convergence of the beam on its first passage through the film being such the film in its second as to bring it to focus on passage.

4. Apparatus as defined in claim 3 including an optical system for rotating the beam of light through an angle of between its two passages through the film.

5. In a system for reproducing sound from a photographic record of the type in which the average transmission varies in accordance with the volume of the recorded sound, an exciter lamp, means passing light from said lamp inthe form of a wide beam through said record, means reflecting said beam and repassing the same in the form of, a narrow beam through said record along substantially the same optical axis, and

a photocell located to be affected by said beam after its second passage through saidrecord.

6. In a system for reproducing sound from a photographic record of the type in which the average transmission varies in accordance with the volume of the recorded sound,. an exciter lamp, a condenser lens focusing light from said lamp in the form of a wide beam and passing the same through said record, a reflector reflecting:

reflecting said beam and repassing the same in the form of a narrow scanning beam through said record along substantially the same optical axis, a photocell located to be affected by saidv beam after its second passage through said rec- 0rd, and a reflector having an area less than that of said wide beam located in said beam and defiecting said narrow beam to said photocell,

. FRITZ STEU'BE. 

